allow using it from the gridview directly

Adjustments code according to the standards.
Adding missing PHPDoc comment.

Need to have a method  `getDataCellContent` to return raw parsed data cell content. This is useful when extending these Columns, for processing any other data before formatting via `renderDataCellContent`.

Fixes #2212: `yii\gridview\DataColumn` generates incorrect labels when used with nosql DB and there is no data

- added example code for application components
- added missing short description

[ci skip]

When we do not want an attribute to be searched we do not define it in
the filter model, or mark it inctive in the scenario when we use the
original model.
GridView should not try to access the attribute then and automatically
not display the filter field.

attribute:type:Header should also affect sort link

default format is text in short format so it should also be
like that in array() defintion.